1. Field of the Invention
The present invention relates to a vehicle alternator equipped with a regulator of an improved adhesion condition between a heat sink and cooling fins, and the vehicle alternator is mounted on a vehicle such as a passenger car or a truck.
2. Description of the Related Art
Recently, the mounting space of a vehicle alternator has become more and more limited because of reduction in engine-mounting space in a vehicle caused by a tendency for a slant-nosed design of the front part of a vehicle for reducing running resistance of a vehicle such as air resistance and the need to enlarge a vehicle compartment space.
Further, in order to increase the fuel consumption of a vehicle, the number of revolutions of or a rotation speed of a vehicle alternator is reduced in an idling condition and the number of revolutions of an engine is also reduced. However, there is on the contrary a strong requirement to further increase the generation capability of an electric power of the vehicle alternator because of electronic loads such as various control devices for use in safety control. Thereby, the demand for a small sized and higher output power vehicle alternator has grown, for example, the size of a stator of a vehicle alternator is 152 mm or less, and the output power of the vehicle alternator is not less than 2.4 kW.
In order to satisfy such a demand, it is necessary to reduce the resistance of a stator winding, to decrease an air gap between a stator and a rotor of a vehicle alternator, and to increase the magnitude of an exciting current. However, the temperature of various components forming the vehicle alternator is thereby increased and the thermal energy thereof deteriorates those components. There are various countermeasures against the increased thermal energy so as to decrease the temperature of the components in the conventional vehicle alternators, namely, to increase the cooling capability thereof. For example, Japanese patent laid open publication NO. JP H7-274440 has disclosed the structure to enhance the cooling capability of a regulator in a vehicle alternator having an improved arrangement of cooling fins. The improved arrangement of the cooling fins mounted on the regulator achieves an adequate flow speed and provides a sufficient amount of flow rate of cooling air. (In particular, see page 2 and is FIG. 1 to FIG. 5 of JP H7-274440)
In general, a heat sink for a regulator is made of copper or copper alloy which has a high thermal conductivity or a high electric conductivity, and cooling fins are made of aluminum from the point of view of easy working and of reducing a manufacturing cost. Still further, silicon adhesive of high thermal resistance is used as bonding agent for bonding the heat sink and the cooling fins. However, because the heat sink is different in material from the cooling fins and those materials have a different thermal expansion coefficient to each other, thermal stress is more increased, in particular, the thermal stress to the adhesive surface between them is more increased by the tendency toward the high output power where both operation are repeated, one is the state of performing the electric power generation of the vehicle alternator driven by an engine of a vehicle and the other is the state of halting the electric power generation. This introduces the difficulty to maintain the adhesion between the cooling fins and the heat sink over a long time and thereby decreases the reliability of the vehicle alternator. The deterioration of the adhesion condition between them causes malfunction of the electric power generation of the vehicle alternator because the radiating capability of the regulator becomes worse.